In a large bowl, mix the chicken legs with the onions, olive oil, fennel seeds, sumac, orange zest and juice, lemon zest and juice, salt, pepper, and cayenne. Cover and leave to marinate for at least 1 hour, preferably overnight, in the fridge.

Preheat the oven to 375 degrees. Transfer the chicken and vegetables to a roasting tray along with sliced fennel. Arrange chicken pieces skin-side up, place orange slices on top, then bake until skin is golden, 35 minutes.

While the chicken is roasting, place the orange juice, red wine vinegar, honey, and star anise, and cinnamon stick in a saucepan over medium heat. Stir, and bring to a boil, reduce the heat, and simmer 30 minutes, until reduced.

Remove the chicken from the oven, spoon a generous amount of orange-anise glaze on to each piece. Turn the oven up to 400 degrees and return to the oven for 5 to 10 minutes, until the chicken is cooked through.

Transfer the chicken to a serving dish and sprinkle on additional sumac and Maldon salt.